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Last Updated: Wednesday, 29 December, 2004, 11:28 GMT
Huygens probe course 'looks good'
Huygens, Nasa/JPL
Light reflected from Huygens makes the probe shine for the cameras
The Huygens probe appears to be on the right course after being unleashed on its journey to Saturn's largest moon Titan, says the US space agency (Nasa).

The Cassini orbiter snapped images of the 2.7m-wide robotic lab as it moved away from its mothership.

Information from the images is helping engineers understand its trajectory, and so far, say Nasa officials, it appears to be right on the mark.

Image analysis will also help narrow down the area where Huygens will land.

In one image, bright spots on Huygens can be seen. These are probably caused by light reflecting off the blanketing material that covers it.

Getaway manoeuvre

Cassini performed a getaway manoeuvre on 28 December to keep it from following its erstwhile passenger into the atmosphere of Titan.

This will also help it establish the required geometry for a communications link during Huygens' descent on 14 January.

Ground controllers received confirmation at 0324GMT on Saturday that the 319kg robot lab had ejected from Cassini.

The probe was released at a gentle, relative speed of 30cm/s and at a spin rate of seven revolutions per minute, which will help stabilise the craft when it enters Titan's atmosphere.

Tension-loaded springs pushed Huygens out on its course to Titan

The probe will coast unguided and unpowered toward Titan until it is woken up by a timer four hours before hitting the top of Titan's atmosphere.

Three parachutes will slow Huygens' descent, giving it about two and a half hours to study its surroundings with a suite of onboard scientific instruments.

If all goes well, the spacecraft will detail the atmosphere's composition, structure, temperature, pressure, winds and aerosols. The camera system will return more than 1,000 images.

Huygens also carries a package of experiments to study Titan's surface, which is currently shrouded in mystery.

It is not certain whether Huygens will make a hard landing on an icy-rocky surface; a squelch into tar-like gunge; or a splash-down in an oily sea.

Huygens diagram (Nasa/Esa)
1. HASI - measures physical and electrical properties of Titan's atmosphere
2. GCMS - identifies and measures chemical species abundant in moon's 'air'
3. ACP - draws in and analyses atmospheric aerosol particles
4. DISR - images descent and investigates light levels
5. DWE - studies direction and strength of Titan's winds
6. SSP - determines physical properties of moon's surface
Titan is the only known planetary satellite with an appreciable atmosphere.

Dominated by nitrogen, methane and other organic (carbon-based) molecules, conditions on this world are thought to resemble those on Earth about 4.5 billion years ago.

As such, scientists hope to see many of the chemical processes that created the conditions in which life developed on our planet (but with temperatures down to -179C, Titan itself is considered too cold to host biology).

It will be some hours later before scientists on Earth learn if the descent through Titan's atmosphere has been a success or a failure.

The Saturnian system is so far from Earth that it takes over an hour for signals to be sent back, even at light-speed.

Launched on 15 October, 1997, Cassini-Huygens went into orbit around Saturn on 1 July this year after a voyage of 3.5 billion km (2.2 billion miles).

Although the short life of Huygens' batteries means nothing will be heard from the probe after 14 January, the mothership Cassini's mission around the Saturnian system will continue for at least another three-and-a-half years.

The $3.2bn mission is a joint venture between Nasa, the European Space Agency (Esa) and the Italian Space Agency (Asi).

How Huygens detached from its mothership

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